As is known in the art, folding a web substrate generally involves the manipulation of the web substrate according to principles of equal path length. Simply stated, the machine direction (MD) folding of a web substrate for equal path lengths requires each cross-machine direction (CD) point of the web substrate to travel an equal geometric distance (equal path geometry) across a folding surface. Thus, each portion of the web substrate is provided with equal tension and proper web tracking. As is known in the art, equal path geometry provides the best processing for a uniform web.
Tearing or the reduction of baggy edges during a folding operation generally requires stopping the folding line to enable personnel to effect manual changes to the equal path geometry. Stoppages result in lost production time and increased production costs. Additionally, manual changes are generally inaccurate and may require additional production stoppage in order to affect further serial, or incremental, equal, or unequal, path geometric changes. Further, a line stoppage requires an entire web substrate processing line be shut down at the parent roll stage. Such a shut down can result in capital losses, due to the inability to produce any intermediate or end products during the period of time the processing line is down.
Equipment for completing folds in high-speed web processes is well known in the art. Folding formers, folding plates, and “V”-folders, and the like, are machined detours and polished sheet metal elements over which a web substrate is guided. A typical “V”-folder would consist of a generally triangular structure that would include a folding plate surface that initially receives the moving web substrate. A folding plate is a generally flat surface with a pair of spaced-apart converging edges. A folding plate typically has a terminal nose surface contiguous to the transition nose surface and merges smoothly therewith forming an oblique angle with it. The terminal nose portion terminates in a point that defines the location of the fold.
Typically, and as is generally known to one of skill in the art, a folding detour generally has a first, or input, angle, α, a second, or side, angle, β, and a third, or resultant, angle, γ, and will generally fold a web substrate along the longitudinal axis of the web substrate. During folding, failure to maintain a proper relationship between the input angle, α, side angle, β, and/or resultant angle, γ, can cause folding equipment stoppages. This is because one edge of the web substrate is longer than the other, and the fold geometry must be adjusted accordingly.
The tendency for a web substrate passing over folding structures to not run or lay flat and straight is generally due to a folding phenomenon hereinafter referred to as a “baggy edge.” A baggy edge can result when one edge of a roll of web stock is physically longer than the other edge. This physically longer, or curved, edge can be demonstrated by rolling out an amount of web material and observing a general “C”-shape, or curve, in the rolled-out portion.
A baggy edge could exist because of either a deviation of strain, stress, or flatness in the web substrate. Additionally, cambered web substrates, common on narrow webs that have been cut from a wide parent roll of web substrate, can also have sufficient deviation to produce a baggy edge in a web substrate folding operation.
A baggy edge, or baggy web substrate, can cause wrinkling during a folding operation due to an insufficient machine direction (MD) tension. This baggy edge may result in a bubble, leaving wrinkles in the folded substrate and causing potentially significant deviations in the ability to laminate or coat, or the lack of ability to produce flat material bonding, or provides difficulties in passing a moving web substrate over flat rollers. This off-quality product requires operator intervention to correct and typically requires the complete shut down of a folding operation and an ensuing loss of production efficiency.
A typical folder is shown in Dutro, U.S. Pat. No. 3,111,310. Dutro discloses a complex series of folding plates for making a fold in a web or ribbon of paper. Curved flanges bound the converging edges of the fold plate and transition nose surfaces. A flue is formed integrally within the flanges. Dutro uses conventional folding plate technology and does not allow for in situ adjustment of the folding plate to reduce a baggy edge in a passing web substrate.
Similarly, other patents show the use of folding plates in various configurations. Exemplary patents include: Great Britain Patent Nos. GB 946,816, GB 1,413,124, and GB 862,296, and U.S. Pat. Nos. 4,131,271; 4,321,051; and 5,779,616. However, none teach or disclose a device that provides continuously adjustable, self-correcting tension on a passing web substrate undergoing folding.
However, because nips are widely used in the industry for laminating, printing, winding, coating and calendaring, it is essential to minimize bagginess, or over-tension, in a moving web substrate. Roisum, Web Bagginess: Making, Measurement and Mitigation Thereof, suggests that line tension can be increased in the machine-direction to remove contraction from the shorter edge of a web to reduce bagginess. Thus, only a machine direction tension is applied to the shorter edge of a web substrate in an attempt to lengthen the shorter edge. However, Roisum also suggests that this method has several limitations and can be difficult to achieve. Most significantly, it is suggested that this technique does not work well with stiff webs that may break before flattening. Additionally, it is suggested that this process may not provide uniform results as small puckers may still occur in the web substrate, resulting in an imperfect edge. Further, the application of additional machine direction tension becomes difficult in application when several web substrates are combined in-line. If one web substrate exhibits properties of non-uniformity, in-line tension must be applied to all webs being combined. To apply tension to only one web of a plurality of combined webs can cause ruffling in the final product, a potentially undesirable end result.
Accordingly, it would be desirable to provide an adjustable, self-correcting web substrate folding system for in situ folding of a web substrate that can provide continuous adjustments to the web substrate folding system prior to web substrate contact with a folding detour. This can minimize web substrate bagginess during folding and yet still provide a high quality finished product.